“Can anyone stop Stockfish?” was the leading question heading into the Swiss. The engine had won Premier Division, the superfinal (with a record-setting performance), and the Cup, and now it had its sights on the Swiss – a tournament it had failed to win last season. Although few would bet against Stockfish in any one-on-one match, the Swiss format did mean that one of Stockfish’s challengers could pip it to the championship if they are able to farm points against weaker engines. Defending Champion Komodo Dragon had managed this feat last season, and it was not impossible that it or Leela Chess Zero might manage again this season.
The Swiss started with a surprise, as League 2 engine Minic took the lead after the first round with a 2-0 win over Vajolet while all the top engines “only” managed at best 1.5-0.5 victories. Minic’s lead lasted for all of one round, as Stockfish, Leela Chess Zero and Komodo Dragon all recorded their own 2-0 victories in the second round. The third round saw a critical match between Stockfish and Komodo Dragon, a match Komodo Dragon needed to hold to have any chance of defending its title – it had failed to defeat ScorpioNN in the first round, and was already half a point behind Stockfish. A tough Caro-Kann line in which Black blocks its own light-square bishop (1. e4 c6 2. c4 e5 3. Nf3 d6) was not what Komodo fans wanted to see, and although Komodo created a near-fortress that humans might have had difficulty breaking down, Stockfish had no trouble. 1.5-0.5 for Stockfish, and Komodo’s hopes of defending its title faded. When Komodo failed to defeat Revenge in the fourth round, its prospects dimmed further.
That left Leela as Stockfish’s closest competitor. Leela had fallen behind in the first round after drawing Koivisto, but it kept up the chase with wins against Stoofvlees and Berserk, remaining only half a point behind Stockfish. The two engines clashed in the fifth round, with Leela wielding the White pieces first. The opening was a dodgy Pirc (1. e4 d6 2. d4 Nf6 3. Nc3 Nc6?!). Stockfish showed the bookmakers just what it thought of 3…Nc6 by meeting 4. d5 with the sad 4…Nb8. That gave White a large development advantage, and as Leela mounted a kingside advance, it seemed that there was a real chance that Leela would win. Nonetheless, Stockfish was unfazed, giving up a pawn to reach a tenable endgame. Leela eventually turned the extra pawn into an extra exchange, but the White king was too exposed for white to make progress while fending off a perpetual.
Now it was Stockfish’s turn to play the White pieces. The stakes were high: if Stockfish were to win, the tournament would be all but over. Leela also met 4. d5 with 4…Nb8, but as Stockfish mounted the same kingside advance that Leela had done, Leela counterattacked with her own queenside play. Stockfish’s evaluation rose dangerously high in response, but Leela had the last laugh as she played a defense Stockfish had missed, yielding a draw. Stockfish continues to lead by half a point, but Leela has won matches against strong opposition that Stockfish has yet to play, so nothing is settled yet. Round six will be crucial, as Leela is paired against Komodo Dragon.
Away from the top boards, the overperformer thus far has been Velvet. Originally finishing 10th in the qualification league, Velvet has beaten League 4 engines Nirvana and Bit Genie to sit comfortably in the middle of the standings. Berserk also continues to impress. Although it lost to Leela, it has won all four of its other matches to go into the sixth round equal 3rd-5th, half a point behind Leela. It will face Stoofvlees – the opponent which eliminated it in the Cup – next, while the last engine on 6.5 points (ScorpioNN) has the unenviable task of facing Stockfish.
